Field of the Invention
The invention relates to a converter for providing a liquid in a measuring line, wherein the liquid is at a measurement pressure corresponding to a rotational speed of a journal rotating about an axis, the journal is slidingly supported in a stationary housing and has a journal bore formed therein from one end of the journal along the axis of rotation; the housing has a first groove which surrounds the journal and communicates with the journal bore through at least one transverse bore in the journal; a flow path for the liquid which can communicate with a reservoir at a primary pressure and with a pressureless sump, includes a throttle, the first groove, the transverse bore and the journal bore; and the measuring line branches off from the path between the transverse bore and the throttle.
Such a converter is also known as an impeller or an rpm-pressure converter. It uses the measurement pressure to furnish a hydraulic signal which is a measure for the rotational speed. Such a converter is applicable in particular to governing the speed of a power engine, especially a steam turbine. To that end, the rotating journal is connected to a driven shaft of the power engine, and the rpm-dependent pressure provided in the measuring line serves to control a device with which the rotational speed can be varied. In the event that the power engine is a steam turbine, that device is, by way of example, a throttle valve or a configuration of a plurality of throttle valves, along with an associated adjusting device. Since the converter provides a hydraulic signal directly, it is especially suitable for inclusion in a hydraulic regulating device of the kind often used in steam turbines.
Converters of the type described at the outset, each being associated with a steam turbine, are found in the book "Steam and Gas Turbines" by B. G. A. Skrotzki and W. A. Vopat, McGraw-Hill Comp., Inc., New York, 1950, chapter 7, pp. 229 ff., and particularly page 240, FIG. 7-18, and page 246, FIG. 7-28. Each of those figures shows a converter of the type described. In each of the converters shown therein, an annular groove (referred to as a "first groove" in the first paragraph above) in a bearing bore of a housing, in which a journal connected to a driven shaft rotates, is supplied with liquid through a further line in which a diaphragm is disposed as a throttle, from a reservoir which in particular is a line system being acted upon at a largely constant primary pressure by a main oil pump. The measuring line, in which the liquid is to be provided at a measurement pressure being dependent on the rpm of the journal, branches off from the groove. The mode of operation of the converter is based on the fact that a flow equilibrium is established between the reservoir and the measuring line, with the equilibrium being dependent on the rpm of the journal. To that end, the journal includes a journal bore, which is formed along its axis of rotation and into which transverse bores, formed approximately perpendicular to the axis of rotation, discharge. Those transverse bores connect the groove to the journal bore. Depending on the rpm of the journal, a more or less large amount of liquid flows through the transverse bores into the outlet bore, and from there flows to a pressureless sump, in other words a collecting tank for the liquid. The outflow of the liquid through the transverse bores is hindered more by centrifugal force as the journal rotates faster. As a result, a pressure arises in the groove from the flow equilibrium being established, that pressure is dependent on the journal rpm and is propagated into the measuring line in the form of the desired measurement pressure. Although the book shows converters having journals which are direct extensions of the given shafts of steam turbines, nevertheless converters of that kind have not proven themselves in practice, since in particular small eccentricities in the positioning of the journal, which are due to the driven shaft play that always exists, excessively impair the function of the converter. Other disadvantages, especially in steam turbines, often reside in the high rotational speeds of the driven shafts, which make it substantially more difficult to dimension the converters. For that reason, in practice converters are not provided directly on the driven shafts but rather on separate shafts, which rotate relatively slowly and are driven by the driven shafts through suitable gears.
The book also explains an inclusion of an rpm-pressure converter in a closed-loop control unit for a steam turbine and hydraulic closed-loop control units in particular are described in detail. The preference for hydraulic control units is based in particular on the fact that a conventional power engine always has a liquid available that is suitable for hydraulic purposes, namely lubricating oil, from a source of adequately high primary pressure, and can thus readily be used to operate a hydraulic control unit.
Other descriptions of closed-loop control units for steam turbines and protected devices, which typically are components of such control units, may be found in German Published, Non-Prosecuted Applications DE 31 38 561 A1 and DE 31 38 562 A1. Details on hydraulic shifting and adjusting members can be found in particular from those references. U.S. Pat. No. 3,395,718 discloses an rpm-pressure converter which, unlike the converters described in the first paragraph above, does not use an essentially stationary flow equilibrium that is dependent on the rpm of the journal. Instead, in it pulses in the form of pressure waves are generated in the liquid, and the predetermined transit time of those waves through a delay line is set into a relation with the variable rpm. After passing through the delay line, the pulses are supplied to a switch formed on the journal, and the switch connects the delay line to the measuring line and the sump in alternation. Depending on the speed of rotation, a more or less large proportion of the pulses arrives in the measuring line. In that way, the measurement pressure which is dependent on the rpm is generated in the measuring line, and a hydraulic actuator is acted upon by that measurement pressure. That converter can be referred to as a "digital" converter, using the conventional vocabulary of electronics, since it primarily processes only certain predetermined unit pulses. A converter of the type described in the first paragraph above, which makes do without pulses, can instead be considered as an "analog" converter. In contrast to the analog converter, such components as throttles are intrinsically entirely foreign to the digital converter.
A converter of the type referred to in the first paragraph above, that is, an analog converter, is also disclosed in German Published, Non-Prosecuted Application DE 17 98 268 A1, corresponding to U.S. Pat. No. 3,473,389. In that converter, the journal bore is widened to make a chamber, from which the liquid that flows in through transverse bores in the journal and part of which flows out through a throttle to a sump, is partly supplied to hydraulic measuring instruments through corresponding lines. The journal rotates in a separate housing and is widened in the manner of a cylindrical can. The entire interior of the housing outside the journal can be considered to be a first groove in the present sense. A second groove encompassing the journal is provided in the housing away from the can-like widening of the journal and the first groove. The second groove communicates through transverse bores and a longitudinal bore with the likewise greatly widened journal bore itself, and from it the measuring line leads to the hydraulic adjusting device.